THURSDAY, June 13 (HealthDay News) -- The world's population could reach nearly 11 billion by 2100, the United Nations predicts, which is about 800 million (8 percent) more than the previous projection of 10.1 billion issued in 2011.

The revised estimate is mostly due to a slower-than-expected decline of birth rates in Africa. The current African population is about 1.1 billion and that is now expected to reach 4.2 billion by the end of the century.

Fewer population changes are expected in other regions of the world. Europe may see a small decline in population due to birth rates that continue to be below replacement level, while some other areas may see slight population increases due to longer life expectancies, said Adrian Raftery, a professor of statistics and sociology at the University of Washington.

Raftery and colleagues at the University of Washington Center for Statistics and Social Sciences developed the statistical methods used in the new U.N. global population estimates.

The projected increase in global population will cause challenges but other pressing matters, such as poverty and climate change, have sidelined the topic. But both of these problems are linked to world population, Raftery said.

"These new findings show that we need to renew policies, such as increasing access to family planning and expanding education for girls, to address rapid population growth in Africa," he said in a university news release.

The world's population passed 6 billion in 1999 and reached 7 billion in 2011, according to the United Nations report, which was issued June 13.